G. V. Bondarenko

The effect of addition of functionalized graphene oxide on the dielectric properties of epoxy composite

The dependence of the complex permittivity of epoxy composite in the microwave region on the concentration of added amine-functionalized graphene fillers is studied. It is shown that the obtained composites have high values of the dielectric loss tangent at comparatively small values of ɛ′.

Synthesis and magnetic properties of Cu3B2O6 single crystals

The temperature dependence of the magnetic susceptibility of Cu3B2O6 single crystals grown by spontaneous crystallization from a melt consisting of a mixture of CuO and B2O3 and the behavior of their magnetization are investigated in magnetic fields up to 55 kOe. A broad susceptibility maximum is observed near 39 K, and a sharp drop in susceptibility is observed at T<10 K. The paramagnetic Néel temperatures for all orientations of the magnetic field in the crystal investigated are negative, attesting to the predominantly antiferromagnetic character of the exchange interactions. The effective magnetic moment of the Cu2+ ion is anisotropic and lies in the range from 1.054μB to 1.545μB. The magnetization depends linearly on magnetic field at T>10 K, whereas at temperatures below 10 K a discontinuity is observed at fields of the order of 40 kOe. At room temperature, electron magnetic resonance characterized by an almost isotropic g factor (g=2.165) is detected at 36.22 GHz. The exchange interactions in Cu3B2O6 are analyzed on the basis of the Goodenough-Kanamori rules. The possibility of the establishment of a singlet magnetic state in the crystal is analyzed.

Size effects and magnetization of (Fe/Si) n multilayer film nanostructures

The temperature dependence of the magnetization of (Fe/Si)n multilayer films with nanometer layers is investigated. The films are prepared through thermal evaporation under ultrahigh vacuum onto Si(100) and Si(111) single-crystal substrates. It is revealed that the thickness of individual iron layers in (Fe/Si)n multilayer films affects the magnetization and its temperature dependence. The inference is made that this dependence is associated with the formation of a chemical interface at the Fe-Si boundaries. The characteristics of the chemical interface in the (Fe/Si)n films are estimated.

Self-propagating high-temperature synthesis in Pt/Co/MgO(001) epitaxial thin films

The self-propagating high-temperature synthesis in the two-layer and multilayer Pt/Co(001) thin films has been investigated. It is shown that the initiation of the synthesis occurs at temperatures of 770–820 K. After the synthesis in the two-layer film samples, the PtCo(001) disordered phase exhibits an epitaxial growth at the interface between cobalt and platinum layers. In the multilayer Pt/Co(001) thin films, the self-propagating high-temperature synthesis also brings about the formation of the PtCo(001) disordered phase on the MgO(001) surface. Further annealing at a temperature of 870 K for 4 h results in the transition of the PtCo(001) disordered phase to the ordered phase. Rapid thermal annealing of the Pt/Co(001) multilayer films at a temperature of 1000 K leads to the formation of the CoPt3 phase. The magnetic characteristics change in accord with the structural transformations in Pt/Co film samples.

Phase transformations in the Mn-Ge system and in GexMn1 − x diluted semiconductors

Results of an X-ray diffraction study as well as magnetic and electrical measurements of the solid-state reactions in Ge/Mn polycrystalline films of an 80/20 atomic composition have been presented. It has been shown that the ferromagnetic Mn5Ge3 phase is formed first on the Ge/Mn interface after annealing at ∼120°C. The further increase in the annealing temperature to 300°C leads to the beginning of the synthesis of the Mn11Ge8 phase, which becomes dominating at 400°C. The existence of new structural transitions in the Mn-Ge system in the region of ∼120 and ∼300°C has been predicted on the basis of the presented results and results obtained earlier when studying solid-state reactions in different film structures. The supposition about the general chemical mechanisms of the synthesis of the Mn5Ge3 and Mn11Ge8 phases during the solid-state reactions in the Ge/Mn films of the 80/20 atomic composition and the phase separation in GexMn1 − x (x > 0.95) diluted semiconductors has been substantiated.

Effect of alloy formation processes in the Co-Cu system on the magnetic and magnetoresistance properties of multilayer Co/Cu films with ultrathin Co layers prepared by DC magnetron sputtering

This paper reports on a study of multilayer Co/Cu films with an effective thickness of the Co layer of ∼3.5 Å, which were prepared by magnetron sputtering. The samples prepared have been found to have a metastable multiphase structure. An analysis of the data obtained by structural and, primarily, by magnetic methods has revealed that the main phases are the Co/Cu supersaturated solid solution (alloy) with a Co concentration of about 30 at %, the superparamagnetic phase, and the paramagnetic phase, which is accounted for by the presence of small (a few atoms at most) Co clusters embedded in the Cu matrix. A clearly pronounced maximum in the temperature dependences of the low-field magnetoresistance has been found, which is associated with the temperature of the magnetic phase transition of the supersaturated Co-Cu alloy.

Kerr rotation and magnetic circular dichroism in Co/SiO2 multilayers

Abstract Kerr rotation and magnetic circular dichroism spectra have been investigated in Co/SiO 2 multilayers in dependence on the dielectric layers thickness. An essential difference has been found between the polar and longitudinal geometries of the experiment. For the polar magnetization of the samples strong changes of the magnetooptical spectra have been observed in comparison with the thick continuous Co film.

Analysis of the structure and magnetic properties of an interface in multilayered (Fe/Si)N nanostructures with the surface-sensitive XMCD method

The structural and magnetic properties of (Fe/Si)N nanostructures obtained by successive deposition on the SiO2/Si(100) surface at a temperature of the substrate of 300 K have been studied. The thicknesses of all Fe and Si layers have been determined by transmission electron microscopy measurements. The magnetic properties have been studied by the X-ray magnetic circular dichroism (XMCD) method near the Fe L3, 2 absorption edges. The orbital (ml) and spin (mS) contributions to the total magnetic moment of iron have been separated. The thicknesses of magnetic and nonmagnetic iron silicide on the Si/Fe and Fe/Si interfaces have been determined with the surface sensitivity of the XMCD method and the model of the interface between the nonmagnetic and weakened magnetic phases.

In situ investigations of magneto-optical properties of thin Fe layers

A thin polycrystalline Fe film on a single-crystal Si substrate with natural SiO2 oxide is obtained by thermal evaporation in ultrahigh vacuum. The magneto-optical properties of the resultant structure are investigated in situ by the methods of spectral ellipsometry. The values of the coercive force for the Fe film are obtained, and the magnetization reversal loop and the energy dependence of the equatorial Kerr effect are constructed. The effectiveness of magnetoellipsometry for in situ analysis of the geometrical and magnetooptical properties of thin ferromagnetic layers is demonstrated.

Long-range chemical interaction in solid-state synthesis: The Kirkendall effect and solid-state reactions in Cu/β-CuZn and Cu/Fe/β-CuZn film systems

The results of the experimental investigations of the solid-state reaction of Cu with β brass, which is associated with the Kirkendall, in Cu/β-CuZn and Cu/Fe/β-CuZn film systems are reported. It has been shown that the initiation temperature of the solid-state synthesis of α brass at the Cu/β-CuZn interface is about 200°C. The chemically inert Fe barrier layers 420 and 850 nm in thickness between the Cu and β-CuZn films do not suppress the solid-state synthesis of the α brass, but increase the initiation temperature to about 250°C. This behavior indicates that the chemical interaction between the Cu and Zn atoms through the chemically inert Fe layer is long-range. The X-ray photoelectron investigations reveal the migration of Zn atoms from the β-CuZn layer through the Fe barrier to the Cu layer. The results are interpreted under the assumption that the migration of Zn atoms in the Kirkendall is initiated by the strong chemical interaction between the Cu and Zn atoms in the Cu and β-CuZn layers, which is due to the synthesis of α brass, rather than by the diffusion random walk, as is commonly accepted at present.